Smell test failures: America’s greenest cities

“percent of people in each city that put their green beliefs into action”

“percentage of people who are willing to admit to no concern or consciousness of environmental issues”

“percent of people who make a conscious effort to recycle”

“Average trips taken on public transport each weekday”

“percent of homes that use solar energy for heating”

These variables were said to be “weighted equally”, and that should set off alarm bells: how do you equally weight variables with different units? You could use ranks, but I bet that isn’t what they did.

Of the top 25 cities, Vegas was 21st in consciousness, 17th= best (i.e. lowest) in unconsciousness, last in recycling, and had no public transport data. But they were first in solar power! Meanwhile, San Francisco was first in consciousness, 4th= best in unconciousness, first in recycling, 2nd in public transit per capita, and 11th in solar. So how did Vegas beat SF overall?

Well, Vegas has a lot of solar power: 0.43% of households, when second-placed Albuquerque was 0.2%, and the median for the top 25 is 0.06. Whatever standardisation they did — perhaps changing to z-scores — left Vegas a huge outlier for solar. So though Vegas sucked in all the other categories, solar alone pushed them to second overall.

Lessons:

Changing to z-scores might not be sensible if your data aren’t normal.